The flexible line is advantageously a flexible pipe intended for conveying a fluid, in particular an underwater pipe capable of receiving a petroleum fluid in order to transfer this fluid from the bottom of a stretch of water to the surface. Such a flexible pipe is for example defined by the API 17J or API RP 17B standard of the American Petroleum Institute (API) and generally comprises from the inside to the outside, a carcass, a pressure sheath, at least one internal pressure-resistance armor for the transported fluid, at least one tensile-strength armor and one external protective sheath.
Alternatively, the flexible line is an umbilical intended for transporting a control fluid, electric power or an information signal. Such an umbilical is for example defined by the general standard API 17E and API RP 17I.
In facilities for exploiting a fluid, intended to collect hydrocarbons in the bottom of a stretch of water, it is known how to connect a bottom assembly to a surface facility by means of a flexible line as defined above.
In order to connect the line onto the surface structure, the line is immersed in the stretch of water, and an upstream end of the line is then moved up towards the surface structure with view to connecting it thereto.
In order to prevent the line from undergoing large torsions or flexures during this installation or during subsequent operation of the facility, the flexible line is engaged through a guide tube secured to the surface structure. This tube is designated by the term of <<I-Tube>> or <<J-Tube>> according to its shape.
During the ascent of the flexible line inside the tube, or during its operational use, outer abrasion of the sheath protecting the flexible line sometimes occurs. This abrasion is for example generated by the friction between the external face of the sheath and the internal face of the protective tube.
In certain critical cases, the abrasion at the surface may generate microcracks or a loss of integrity of the protective sheath, also called an external sheath. In this case, the metal elements located inside the sheath, and in particular the tensile armors, are capable of being corroded, which may have significant consequences on the mechanical strength of the flexible line over time.
It is therefore necessary to be able to easily check the mechanical integrity of such a pipe, in particular after introducing it in a protective tube, since any accessibility to the pipe then becomes impossible. Visual inspection is impossible for the portion of the pipe located in the protective tube.
WO2009/070769 describes a measurement method in which an optical sensor, formed by an optical fiber is integrated into the internal structure of a flexible pipe.
Optical measurements made on the optical fiber give the possibility of determining whether this fiber is mechanically degraded.
Such a method is however complicated and expensive to apply, since it requires an enhanced optical apparatus.